| The manganese oxides ABO3 with perovskite structure have aroused a great deal of interest due to their various properties and strong correlation among charge, spin, orbit and lattice. This coupling effect is considered to be wide application for a series of new physical phenomena such as insulation-metal transition and phase separation. We synthesized Smo.5Cao.5Mn1-xFexO3 series in stoichiometric of x= 0,0.025,0.05,0.075,0.10,0.15,0.20, 0.30 and performed measurements of crystal structure and magnetic properties to study their various properties.In this paper, the Smo.5Ca0.5Mn1-xFexO3 compounds were prepared using a standard ceramic process, powder x-ray diffraction and infrared absorption spectrum were performed to characterize the structure of samples. Our results show that each sample has a pure phase of orthorhombic perovskite structure.The magnetic measurements (M-T, M-H) were performed by physical property measurement system (PPMS) for the sample series. In the parent sample, there are two valence state for manganese ion, i.e., trivalence and tetravalence. The results show that charge order phenomenon and ferromagnetic clusters most probable appeared at the ratio of Mn3+:Mn4+ 1:1 and the parent phase displays the characteristics existing in both the glassy state and phase separation system below charge order temperature. The distribution of ferromagnetic clusters is random as the ferromagnetism induced by carrier double-exchange is random, due to the randomness replacement of Fe in the lattice. The charge order state is restrained with the increasing concentration of Fe. A bifurcation arises at the irreversibility temperature (Tirr) between the zero-field-cooled (ZFC) and field-cooled (FC) curves. We explained this as follows, the spin direction of magnetic ions induced by doping distributes randomness in the ZFC process and there does not exist long range magnetic order in this state. While this order appears in the FC process due to the moments of magnetic ions can be realigned by the variation of external magnetic field, and the magnetic order is gradually frozen with the decreasing temperature. In the ZFC curve, the magnetization decreases gradually after it reach the maximum below the irreversibility temperature for all samples. This is the result of competition between ferromagnetic clusters and antiferromagnetic clusters and it is a typical characteristic of phase separation. However, the magnetization at T-2 K increases gradually with the increasing concentration of Fe until x= 0.10, then it decreases as the doping increased. It indicates that the antiferromagnetic order is restrained by Fe doping which enhances the ferromagnetic order, the effect reduces after it reaches the maximum at x= 0.10. The M-H curves exhibit slight hysteresis for all samples, and the hysteresis is more distinct with the increasing concentration of doping. This further corroborates the existence of ferromagnetic phase in the samples. However, the magnetization of M-H loops do not display any saturation until the magnetic field reached 8 T for all samples, which indicated that the content of ferromagnetic components is very low. The antiferromagnetic order dominates the magnetic order of the series of samples and the slightly ferromagnetic components are the realigned of cluster spin in a short range which is induced by doping, just as in the parent sample. The ferromagnetic components increase with the increase of Fe and compete with antiferromagnetic components. |
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